1. Field of the Invention
The present invention relates generally to a single-wheel cart and, more particularly, to a motor-assisted single-wheel cart wherein an assist force corresponding to an operator's hand operational force is produced by a motor and applied to a wheel of the cart to thereby lighten the operational force.
2. Description of the Related Art
A hand-pushed single-wheel cart, also called a wheelbarrow, is used at various places including construction spots and farmland since it is small and capable of making sharp turns. The single-wheel cart with such a simple arrangement requires an operator to bear a considerable burden when carrying a heavy article thereon and climbing up a slope.
To reduce such an operator's burden, one may propose a single-wheel cart which is self-propelled by a motive power. Such self-propelled carts are known from, for example, Japanese Utility Model Laid-Open Publication No. SHO-62-196736 entitled "APPARATUS FOR CONTROLLING PROPELLING OR POWERED SINGLE-WHEEL CART" and Japanese Utility Model Publication No. SHO-51-39970 entitled "ELECTRIC CART".
The powered single-wheel cart disclosed in Japanese Utility Model Laid-Open Publication No. SHO-62-196736 is constructed so as to drive a single wheel through a belt and a centrifugal clutch by a motor comprised of an engine, as shown in FIG. 1 of the publication. Further, in the powered single-wheel cart, a throttle lever is provided at an end portion of a handle extending rearwardly upwardly from a bed frame and a rotational speed of the motor is controlled by operating the throttle lever. Since the powered single-wheel cart is self-propelled, the operator's burden is lightened when carrying a heavy article thereon and climbing up a slope. However, on the contrary, mobility and usability are no better than the hand-pushed single-wheel cart. At construction sites and in a plant culture house covered with a vinyl, for example, since there is a ground unevenness in addition to a work space being narrow, it is necessary to frequently adjust a propelling speed and a propelling direction of the single-wheel cart. For this use, the powered single-wheel cart leaves room for further improvements.
The powered single-wheel cart is not suitable for an operational environment within the culture house due to an exhaust gas and engine sounds. Further, a certain degree of skill is required for controlling an output force of the engine.
Further, the powered single-wheel cart is construction such that the motor is disposed in a low and narrow space below the bed frame, so that it is hard to perform a maintenance and inspection operation for the motor. Still further, when the powered single-wheel cart is used in a muddy place, care must be taken to prevent water from entering the motor disposed in a low position. When the motor is arranged on the bed frame, a center of gravity of the powered single-wheel cart is placed at a high position while the space for the bed frame becomes narrow.
The motor cart disclosed in Japanese Utility Model Publication SHO-51-39970 is constructed such that right and left front wheels and a caster rear wheel are mounted below a base plate for a bed and the front wheels are driven by a reversible motor for driving, as shown in FIGS. 1 and 2 of the publication.
Also in the motor cart, mobility and usability are no better than the hand-pushed single cart. Further, in the motor cart, in addition to the reversible motor, it is necessary to mount a heavy battery and a heavy box body installing electrical control devices therein. Even where the motor cart is modified to a single-wheel cart, as heavy articles such as the reversible motor and the battery are simply mounted, there is a risk that operability of the single-wheel cart goes down.
Further, since the motor cart is constructed such that the reversible motor for driving is arranged in the low and narrow space below the base plate for the bed, it is hard to perform a maintenance and inspection operation of the reversible motor. Further, it becomes necessary to take care for preventing water from entering the reversible motor disposed in the low position.
Still another self-propelled cart is known from Japanese Utility Model Laid-Open Publication HEI-2-108679 entitled "SINGLE-WHEEL CART WITH MOTOR".
In the motor-equipped single-wheel cart just mentioned, a single wheel is driven by an internal combustion engine or a battery-powered electric motor through a reduction gear and a power transmission chain, as shown in FIG. 1 of the publication. The internal combustion engine or the battery-powered electric motor, the reduction gear and the wheel are mounted to a pipe frame below the bed.
However, since the single-wheel cart with the motor is arranged in such a manner as to transmit an output of the internal combustion engine or the battery-powered motor to the wheel and a height of the bed is increased in accordance with a diameter of a sprocket, there are problems such that it is troublesome to load and unload a cargo on board, that a maintenance and inspection operation is required for periodically adjusting an extension of the power transmission chain, and that it is easily affected by a mud splash during operation and the like.
Further, in the motor-carrying single-wheel cart, for taking off the wheel from the pipe frame, the power transmission chain must be taken off first. Accordingly, tire changing becomes tedious and time-consuming.